Vultures have keen eyesight. It is believed they are able to spot a three-foot carcass from four miles away on the open plains. In some species, when an individual sees a carcass it begins to circle above it. This draws the attention of other vultures that then join in. (Source)

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I will post every week “Thursday Twitters”, pictures of birds mainly from
Finland and Southern Africa, occasionally also taken elsewhere.
The source of the text is most likely Wikipedia or similar online article.